What are the physical and chemical properties of natural quartz?

Physical Properties

• Hardness: Quartz has a Mohs hardness of 7, which means it is relatively hard and can scratch most common materials. It is harder than materials like feldspar and calcite, and is comparable in hardness to topaz123.
• Crystal Structure: It belongs to the trigonal crystal system, usually presenting as a hexagonal prism shape with pyramidal terminations at the ends. In rocks, it is often found as anhedral grains12.
• Transparency: It can be transparent to translucent. Pure quartz is colorless and transparent, but due to the presence of impurities or inclusions, it can exhibit various colors such as white, gray, purple, pink, yellow, brown, etc12.
• Luster: Quartz has a vitreous (glassy) luster on its surface, and the fracture shows a greasy luster12.
• Density: Its density is approximately 2.65 grams per cubic centimeter12.
• Refractive Index: The refractive index ranges from 1.544 to 1.553, and the double refractive index is 0.0091.
• Piezoelectricity: Quartz crystals possess piezoelectric properties, which means they can generate an electric charge when subjected to mechanical stress, and vice versa12.
• Thermal Conductivity: The thermal conductivity of crystalline quartz decreases with increasing temperature, while that of amorphous quartz increases with temperature1.
• Color: Quartz occurs in a wide variety of colors, including common ones like colorless, white, gray, purple, yellow, brown, black, pink, and green. The coloration is mainly due to the presence of trace elements or impurities such as iron, titanium, aluminum, etc12.

Chemical Properties

• Chemical Composition: The main chemical component of quartz is silicon dioxide (SiO₂), with trace amounts of impurity elements such as iron (Fe), titanium (Ti), aluminum (Al), potassium (K), sodium (Na), and germanium (Ge)12.
• Stability: Quartz is chemically stable and does not dissolve in water or most acids under normal conditions. However, it can react with hydrofluoric acid, and can also be slowly corroded by concentrated phosphoric acid12.
• Solubility: It is slightly soluble in potassium hydroxide (KOH) solution and 1,2-dihydroxybenzene